The effect of various additives of Cl−, Br−, and I− on the potential of a passivated steel electrode was established. In solutions of Na2CrO4, Na2HPO4, and Na2WO4, S-shaped relations were obtained between the steady-state potential and the quantity of the aggressive salt added. The resulting active potentials were established after an induction period which decreases with increase in the concentration of the attacking ions and/or decrease in that of the inhibiting anions. The concentration, Cagg, that can be tolerated by a certain concentration of the inhibiting anion, Cinh, is given by logCinh=K+nlogCagg, where K and n are constants. The equation was derived theoretically on the basis of the changes produced in the structure of the double layer caused by specific adsorption of both aggressive and passivating ions. In solutions of KMnO4, NaNO2, and K3[(Fe(CN)6)], the passivating film could not withstand the corroding action of the halide ions.
The potentiodynamic anodic polarization curves for the lead electrode were obtained in 0.1 mol L‐1 KOH solution in the absence and presence of C103‐ or C104‐ as aggressive ions at different concentrations. Lower concentrations of these ions have no significant influence on the passive film, while higher concentrations raise the active dissolution current density, and cause destruction of passivity and initiation of pitting corrosion. The critical pitting corrosion potential varies with the concentration of the aggressive ions according to sigmoidal curves. These curves were explained on the basis of the formation of passivitable, active and continuously propagagting pits depending on the range of the aggressive ion concentration. Additions of increasing concentrations of chromate, phosphate, sulphate and carbonate ions cause a shift of the critical pitting potential in the noble direction accounting for increase resistance to pitting attack (inhibition). The pitting corrosion potential varies with the concentration of the inhibitive ions, in the presence of a constant concentration of the aggressive ions, according to curves of sigmoidal shape. From these curves one can determine the minimum concentration of the inhibitive ions necessary for inhibition of pitting corrosion to occur.
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